Metalizing compositions



May 28, 1968 L. c. HOFFMAN 3,385,799

METALIZING COMPOSITIONS Filed Nov. 9, 1965 2 Sheets-Sheet 1 SOLDERABLEMIXTURE COMPOSITIONS SOLOERABLE ALLOY COMPOSITIONS Q o I VITREOUS M WPLATINUM BINDER 0 F I G 1 m0 cow SOLOERABLE MIXTURE COMPOSITIONSSOLOERABLE ALLOY COMPOSITIONS VITREOUS BINDER mo '00 PALLAOIUM F I G. 2

INVENTOR LEWIS C. HOFFMAN I ATTORNEY y 28, I968. L. c. HOFFMAN I3,385,799

METALIZING COMPOSITIONS Filed Nov. 9, i965 2 Sheets-Sheet 2 LA? 71575 MVH5 AEWAS C ATTORNEY United States Patent 3,385,799 METALIZINGCOMPOSITIONS Lewis C. Hoffman, Wilmington, Del., assignor to E. I. (illPont de Nemonrs and Company, Wilmington, Del., a corporation of DelawareContinuation-impart of application Ser. No. 258,606,

Feb. 14, 1963. This application Nov. 9, 1965, Ser.

12 Claims. (Cl. 252514) This invention is a continuation-in-part of mycopending application, Ser. No. 258,606, filed Feb. 14, 1963.

This invention relates to metalizing compositions useful for the formingof electrically conductive paths, electrically resistive paths andcapacitor electrodes on electrically insulative and/or dielectricsubstrates. The metalizing compositions of this invention arecharacterized in that they provide for the production of electricelements having mechanical and electrical properties not heretoforeattained.

Metalizing compositions used with prefired ceramic substrates to formelectrical elements customarily contain powdered vitreous binder, finelydivided noble metal particles and an inert vehicle. A major purpose ofthe vitreous binder is to secure the noble metal particles to theceramic substrate. To provide this function, a firing temperature mustbe employed which causes the vitreous binder to soften and wet theceramic substrate. It has been observed that higher adhesive values canbe obtained with higher firing temperatures. However, when temperaturesequal to or in excess of the melting point of the noble metal particlesof the metalizing composition are used for firing, the metal particlesdraw back into globules forming non-continuous fired-on coatings anddefective electrical elements. To avoid the formation of these undesiredmetal globules while using metalizing compositions containing the moreabundant and less expensive noble metals such as gold and silver whichmelt at 1062 C. and 960 C. repsectively, vitreous binders which meltbelow these temperatures are used. The industry has recently demandedelectrical elements which cannot be produced using these prior artmaterials.

Capacitors fabricated with ceramic dielectric layers are customarilyproduced by spraying slurries of the finely divided ceramic dielectriconto a base surface, drying the same, and then superimposing thereon afinely divided noble metal, e.g., silver, in a vehicle, in paste form.This is usually done by screen-stencilling the silver paste onto thedielectric layer in a desired pattern, later to serve as the capacitorelectrode. As many as 40 alternate layers of ceramic dielectric andsilver electrodes may be built in this manner, for example, as shown inU.Sv Patents Nos. 2,389,420 and 2,389,176. The so-formed compositestructure is then fired at the fusing temperature of the ceramic to forman electrical capacitor unit. With glass ceramic dielectric the fusingtemperature of the dielectric layer is of the order of 700 C. to 800 C.and silver is a suitable and desirable electrode material since suchfiring temperature is below the melting point of silver.

The industry has more recently demanded a dielectric material having ahigher dielectric constant than that of glass ceramic. It has becomenecessary to form the dielectric of a material having a much higherfusing temperature than that of glass. Substances such as barium orstrontium titanate or titanium dioxide, having a sintering temperatureof over 1350 C. are necessary for this purpose. With such dielectrics,neither finely divided silver nor gold can be used since at fusingtemperatures of over 1200 C., silver and gold draw into fine globulesand produce non-continuous electrode layers. This means that theelectrode screen-stencil paste for use 'with these mate- "ice rials hasnecessarily been composed of metal powders of platinum, palladium orsimilarly expensive noble metals, the only materials heretoforeavailable.

It is an object of this invention to provide metalizing compositionswhich will enable the production of electrical elements havingmechanical and electrical qualities superior to those heretoforeproduced.

It is a further object of this invention to provide metalizingcompositions which can be fired to higher temperatures than can priorart mctalizing compositions of similar cost.

It is a further object of this invention to provide metalizingcompositions which will enable the use of high sintering temperaturedielectric material.

It is a further object of this invention to provide new and improvedmetalizing compositions for use in producing ceramic fired capacitors inwhich the ceramic material has a high fusing temperature, i.e., a fusingtemperature over 1200 C.

It is a still further object of this invention to provide metalizingcompositions comprising powdered vitreous binders which, by reason oftheir high sintering temperatures, could not be used with metalizingcompositions containing particles of pure silver and/ or pure gold.

These and other objects will occur to those skilled in the art readingthe following detailed disclosure. I

The objects of the invention may be accomplished, in general, byproviding metalizing compositions which contain powders of noble metalalloys which consist essentially of two noble metals selected from thegroup consisting of gold, silver, platinum and palladium. Specifically,the alloy powders of the metalizing compositions of this invention aresilver-gold, silver-platinum, silver-palladium, gold-platinum,gold-palladium and platinum-palladium alloys. The alloy metals in themetalizing compositions of this invention are characterized in that themetal components thereof form continuous series of solid solutionsthroughout the entire range of alloy compositions without the formationof compounds or eutectics.

The noble metal component of the metalizing composition of thisinvention will be in finely divided form, i.e., a powder sufficientlyfinely divided to pass through a 325 mesh (US. Standard Sieve Scale)stencil screen. Generally, the powder will have an average particle sizenot exceeding 40 microns with no more than 5% of the particles beinglarger than 42 microns. Desirably, the average particle size will notexceed about 5 microns and, preferably, will be in the range 0.1 to 0.5micron. The most preferred powders will be essentially free of particlesof a size greater than about 5 microns; with an average particle size inthe range 0.1 to 0.5 micron.

In preparing the metalizing com-positions of this invention, the alloypowders prepared by the method disclosed in my copending application,Ser. No. 507,038, filed of even date herewith can be used. The method ofthe said copending application is the only practical way known toapplicant for preparing these alloy powders. By this meth- 0d, the alloypowder is precipitated from a solution of dissolved compounds of themetal constituents of the alloy to be formed by adding thereto areducing agent which will simultaneously reduce both met-a1 constituentsof the alloy to their metals and coprecipitate the desired alloyparticles.

The following examples are given to illustrate in detail the method ofpreparing alloy particles in accordance with the teachings of saidapplication, Ser. No. 507,038; it being understood that these detailsare not to be taken as limitations of this invention.

Example I To obtain a gold-10% platinum alloy, 24 grams of a PtCl,solution containing 32.67% platinum by analysis were mixed with 176grams of an AuCl solution containing 39.09% gold. The resulting solutionwas diluted to 2500 ml. and a solution of 50 grams of hydrazine hydratein 1000 ml. of deionized water was dropped in with rapid stirring. Ablack precipitate of the gold and platinum alloy formed which wasallowed to settle, washed with water by decantation, filtered off anddried. The observed melting point of this precipitate was 1080 C. whichcoincided with the theoretical melting point of a 90% gold-10% platinumalloy as obtained from the literature. The average particle size of thisprecipitate powder was 0.3 micron.

Example 2 15 grams of a PdCl solution containing 26% palladium byanalysis were mixed with 85 grams of an AuCl solut-ion containing 39.08%gold so that the weight of pa lladium in the resulting solution equalled10% of the total weight of palladium and gold. The resulting solutionwas diluted to 250 ml. and a solution of 4 grams of hydrazine hydrate in100 ml. of deionized water was dropped in with rapid stirring. A blackprecipitate of the gold-palladium alloy formed which was allowed tosettle, washed with water by decantation, filtered off and dried. Themelting point of this precipitate was observed to be 1175 C. whichdiffered from the theoretical melting point of a 90% gold-10% palladiumalloy by only 25 C. The observed melting point was 113 C. above themelting point of gold.

Example 3 310 grams of palladium sponge are dissolved in 5 liters ofred, fuming nitric acid (Sp. gr. 1.53 g./cc.) at 50-60 C. The solutionis allowed to cool. 77.5 grams of silver are then dissolved in thesolution to give an 80/20 weight ratio of Pd/Ag in the solution. 7.1liters of concentrated ammonium hydroxide (Sp. gr. 0.9) are then slowlydropped into the solution changing the solution from brown through redand yellow to yellow-green. The pH of the solution is about 5.5.

1 liter of 50% H PO solution is next slowly dropped int-o the abovesolution. A black precipitate forms and settles to the bottom of thereaction vessel. The precipitate is filtered off and dried, yielding386.5 grams of alloy powder.

The powder has a melting point of about 1400 C., showing that it is analloy of Pd and Ag rather than a mixture of the two. The averageparticle size of this powder is about 0.4 micron.

By varying the relaive amounts of the solutions of the metal compoundsused in Examples 1, 2 and 3 above, alloy particles were prepared by themethod of these examples having metal ratios which difiered from themetal ratios of the alloys of Examples 1, 2 and 3. For further detailsregarding the materials used and the method of making these alloypowders, reference can be made to my copending application, Ser. No.507,038.

Tables I and II set forth below the particle size distributions of thepowders of Examples 1 and 2 respectively. The powders of these twoexamples have average particle sizes and particle size distributionswhich are typical of the alloy powders made in accordance with themethod of my copending application, Ser. No. 507,038. These particlesize analyses were obtained by microscopic study of enlarged electronphotomicrographs of the respective powders.

TABLE I.GOLDPLATINUM ALLOY POWDER Percentage of particles Particle sizerange: within indicated size range 0-0.1 micron 2 2.0-5.0 microns 40.1-1.0 micron 80 O 1.0-2.0 microns 9 5.0-10.0 microns 3 Greater than10.0 microns 1 The average particle size was 0.3 micron.

. 4 v 7 TABLE II.GOLD-IALLADIUM ALLOY POWDER Percentage of particlesParticle size range: within indicated size range 0-0.1 micron None0.1-1.0 micron 1.0-2.0 microns l5 2.0-5.0 microns 4 5.0-10.0 microns 4Greater than 10.0 microns 2 The average particle size was 0.2 micron.

These alloy powders are characterized in being irregularly shaped, andhaving a small average size resulting in a high surface area to massratio and excellent conductive properties. The particles of the powders,most importantly the surface portions thereof, consist of homogeneousmixtures of the atoms of the alloy metals. By reason of the fact that bycount of the particles are within a close, small size range, between 0.1and 5.0 microns, setting and vertial classification of the particlesduring application and firing of the metalizing compositions arereduced. More uniform, high quality fired-on coatings can accordingly beproduced with the metal powders of this invention. Average particlesizes of about 40 microns and smaller are necessary to enable screenprinting through 325 mesh screens.

To illustrate the distinguishing features of this invention, the resultsof an attempt to produce an alloy powder acceptable for use inmetallizing compositions by a technique presently known to themetalizing industry is here reported. An alloy powder consisting ofplatinum and gold which was comminuted from a thermally prepared alloybutton of these metals, most closely approached the desired propertiesnecessary in an alloy power which is to be used in a metalizingcompound. The average particle size and particle size distribution ofthis alloy powder are set forth in Table III hereinafter. The sizedistribution was determined by the same microscopic analysis which wasused to obtain the data in Tables I and II above.

TABLE III.GOLD-PLATINUM ALLOY (MECHANICALLY COMMINUTED) Percentage ofparticles Particle size range: within indicated size range The averageparticle size was 62 microns.

The gross inadequacy of this mechanically comminuted powder wasdemonstrated by its lack of plasticity when mixed with a typical vehicle(8% solution of ethylcellulose in beta-terpineol) and its inability topass through the fine 200-325 mesh screens used in screen-stencilling.

In addition to the metal alloy powders, the metalizing compositions ofthis invention comprise an inert vehicle. Any inert liquid may beemployed for this purpose. Preferably an organic solvent with or withoutthickening agents, stabilizing agents or the like is used as thevehicle. For example, methyl, ethyl, propyl, butyl or higher alcohols,the corresponding esters of such alcohols such as their acetates,propionates, etc., the terpenes and liquid resins, for example, pineoil, alpha-terpineol, beta-terpinelo and the like and other inertliquids may be used, the function of the liquid being mainly to form aliquid or paste of the desired viscosity for application purposes. Thevehicles may contain or be composed of volatile liquid to promote fastdrying after application, or they may contain waxes, thermoplasticresins or wax-like materials which are solid at room temperature butthermofluid by nature, whereby the metalizing compositions may beapplied at an elevated temperature to set immediately upon contact withthe cooler substrate to which they are applied.

As thickening agents, polymers such as methacrylate andbutylmethacrylate resins, ethylcellulose and the like may be employed.Of the many vehicles usable in this invention, an 8% solution ofethylcellose in beta-terpineol and a solution of ethylcellulose in butylCellosolve acetate are preferred. Butyl Cellosolve acetate is themonobutyl ether monoacetate of ethylene glycol. whose formula is C H-O-CH OOCCH While metalizing compositions which are applied to green(unfired) dielectric substrates customarily consist essentially of metalpowder and a vehicle, the metalizing compositions which are applied toperified ceramic substrates contain a vitreous binder in addition to themetal powder and inert vehicle. Metalizing compositions containingvitreous binders are most suitable for the formation of conductive andresistive paths of ceramic substrates. The viterous binders used in themetalizing compositions of this invention can be composed of any glassor ceramic material which will melt at a temperature lower than themelting point of the alloy powder with which it is used and which willadhere well to the substrate onto which the metalizing composition isapplied. The high melting point alloy powders used in the metalizingcompositions of this invention will enable the metalizing compositionsto be fired to higher temperatures than those which can be used withmixtures of pure metal particles of the two constituents of thecorresponding alloys. It has been observed that greater adhesion to thesubstrate can be achieved with the higher firing temperatures which aremade possible for the use of alloy powders.

Typical vitreous binders usable in the metalizing compositions of thisinvention are lead, cadmium, barium, calcium, or other borate orborosilicate glass frits.

The vitreous binders used in the metalizing compositions of thisinvention may be composed only of frit or may in addition include zincoxide, magnesium oxide, bismuth oxide or lead oxide. It has been foundthat the addition of bismuth oxide to frit will permit improvedsolderability and resistance properties of conductor compositions.Moreover, such addition will permit much greater variation of firingconditions and temperatures without altering metalizing properties.

The preparation of such frits is well known and consists, for example,in melting together batch ingredients which will yield the desiredoxides under the fusing conditions of frit production, i.e., boric oxidecan be obtained from boric acid, silicon dioxide can be produced fromflint, lead oxide can be produced from red lead or white lead, bariumoxide can be produced from barium carbonate, etc., and pouring themolten composition into water to form the frit. The coarse frit producedin this manner is preferably milled for 2 to 20 hours, for example, in aball mill with water until it has been reduced to a size approximatelythe same as the alloy powder with which it is to be used, i.e., to apowder having an average particle size of from 3 to 30 microns andpreferably from 10 to 20 microns.

In formulating vitreous binders which consist of cadmium borate frit andbismuth oxide, ratios of these materials within the range of 0.5 to 10parts of cadmium borate frit for every 2 to parts of bismuth oxide arerecommended. The cadmium borate frit may be prepared by melting togethermixtures of cadmium oxide and boric acid, where the amount of cadmiumoxide constitutes from 75 to 95% of the total amount of materialpresent. Preferably, the metalizing compositions of this inventioninclude as the vitreous binder component, cadmium borate frit andbismuth oxide in the preferred ratio of 2.24 parts of cadmium boratefrit and 8.96 parts of bismuth oxide with cadmium borate frit consistingof 79 parts of cadmium oxide and 21 parts of boron oxide. This preferredvitreous binder in used in the metalizing compositions in a number ofthe examples set forth hereinafter.

Other frits which can be used as the vitreous binder component are setforth in Table IV below.

Still another vitreous binder usable in conjunction with the alloypowders of this invention consists essentially of 3.9 parts of CaO, 0.8part BaO, 27.7 parts ZnO, 21.7 parts of SiO 26.7 parts of B 0 8.7 partsof Na O, 0.7 part of PbO, 5.8 parts of Al O and 4.0 parts of Zr O. Thisbinder is especially suited for use in metalizing compositions for theprinting of resistive paths.

The metalizing compositions of this invention can be used with presentlyavailable substrates including those composed of forsterite, steatite,titanium dioxide, barium titanate, alumina or zircon porcelain. Todemonstrate the invention, metalizing compositions have been applied toalumina substrates, known commercially as AlSiMag 614.

Metalizing compositions of this invention which are to be used to formcapacitors, resistors and conductors which are not to be soldered mayinclude noble metal aalloy particles containing 5% to 9 5% of eithermetal. Metalizing compositions which are to be used in the formation ofconductors which are to be soldered should not contain alloy particlesin which the ratio of metals results in non-solderability. Generally,the content of one of the metals in the alloy should be within the rangeof from about 12.5% to 87.5%. Platinum should not be present in thealloy in amounts greater than or less than about 15% when alloyed withsilver or gold or less than about 10% when alloyed with palladium.Palladium should be present in alloys of gold or silver in amountswithin the range of 10 to 85%. Alloyed with gold, the amount of silverpresent in the alloy should be within the range of 15 to 85%.

When vitreous binders are present in metalizing compositions, theyshould always be present in sufficient quantities to provide adequateadhesion, for example, in amounts equal to or in excess of 2.5 of thecombined amount of alloy powder and vitreous binder, also known as thesolids content of the metalizing composition. The amount of vitreousbinder present can constitute as high as of the solids content of themetalizing composition. Metalizing compositions of this inventionwherein the vitreous binders constitute from 20% to 30% of the solidscontent may be used to form large cross-sectional, conductive paths orthin cross-sectional resistive paths. In metalizing compositions to beused in the formation of solderable conductors the percentage ofvitreous binder in the solids content of the compositions should bewithin the range of 5% to 30% for all platinum alloys, within the rangeof 5% to 25% for the gold-palladium alloy, and Within the range of 5% to20% for silver-gold and silver-palladium alloys.

-The amount of inert vehicle present in the metalizing compositions canvary widely depending, to a large extent, on the method of application,percentage values within the range of 10 to 70 have been satisfactory inapplying the metalizing compositions of this invention.

F IGURE l is a three-component diagram of gold, platinum and vitreousbinder and illustrates the solderable mixtures of pure gold particles,pure platinum particles and vitreous binders as well as the solderablemixtures of gold-platinum alloy powder and vitreous binder.

FIGURE 2 is a three-component diagram-of gold,

palladium and vitreous binder and illustrates the solderable mixtures ofpure gold particles, pure palladium particles and vitreous binders aswell as the solderable mixtures of gold-palladium alloy powder andvitreous binder.

FIGURE 3 of the drawing shows a section in elevation of a capacitorwhich can be made in accordance with this invention.

FIGURE 4 shOWs a cross-section view of the capacitor of FIGURE 3 takenalong the line of 4-4 of FIGURE 3.

To demonstrate the present invention, a plurality of metalizingcompositions were prepared using as the vehicle an 8% solution ofethylcellulose in beta-terpineol, and the preferred vitreous binderconsisting of cadmium borate frit and bismuth oxide. Metal alloy powdersof gold and platinum wherein the percentage of platinum present was 10%,21.4%, 30%, 50%, 60%, 70%, 80% and 90% and metal alloy powders of goldand palladium wherein the percentage of palladium present was 10%, 70%,80% and 90%, were prepared and combined with the preferred vitreousbinder and vehicle. The resulting metalizing compositions consisted of67% solids and 33% organic vehicle. Different ratios of metal alloypowder to vitreous binder were used to form the solids component of themetalizing composition with the metal alloy powder percentages of thesolids being 5%, 10%, 20%, 30%, 40%, 60%. 70%, and

Since the mechanically comminuted metal alloy of Table III could not bescreen printed, noble metal powders consisting of mixtures of pure goldparticles and pure platinum particles, and noble metal powdersconsisting of pure gold particles and pure palladium particles wereprepared and were mixed with the preferred binder and vehicle all in thesame proportions as were the components of the metalizing compositionswhich contained the noble metal alloy powders. All of these metalizingcompositions were screen-stencilled onto alumina substrates (AlSiMag614), were fired and dip-soldered as is well known in the metalizing artto form electrical elements. To provide as fair a basis of comparison aspossible, all of the metalizing compositions were fired for two minutesat the same temperature, namely 1050 C., the highest temperature atwhich the powders containing pure gold particles could be fired.solderability was initially determined by optical examination afterdipping into a 67/33 Sn-Pb solder at 200- 210" C. for approximately 60seconds. Adhesion and solderability were determined by soldering on a0.025 inch tinned copper connecting wire and pulling 01f the wire withan Instron tester in peel. The tested sample was then observed todetermine whether the failure occurred in adhesion at the conductivelayer-alumina interface or in solderability at the wire-conductive layerjoint.

The areas in FIGURES 1 and 2 labeled solderable mixture compositions andsolderable alloy compositions contain all those metalizing compositionswhich had acceptable adhesive, solderability and conductivecharacteristics. The bond of the metalizing composition to the aluminasubstrate and the bond of the copper lead to the conductive layer eachwithstood peel tensions of 750 p.s.i. None of the samples fired at 1050C. successfully withstood peel tensions in excess of 2,200 p.s.i. It canbe seen from a mere inspection of these FIG- URES that a greaterlattitude of metalizing compositions is made available through the useof alloy powders. Metalizing compositions comprising alloy powdershaving vitreous binder contents greater than those falling within theindicated area of solderable alloy compositions did not possessacceptable solderability qualities. Metalizing compositions havingconcentrations of platinum and palladium greater than those fallingwithin the indicated area of solderable alloy compositions also tendedto result in non-solderability. Concentrations of gold in excess of theconcentrations which lie within the solderable composition area tend toresult in too rapid solubility of the metal particles in the solder bathwith resulting failure to solder. It was observed that vitreous binderconcentrations less than the amounts in the solderable alloycompositions area gave inferior adhesion.

Additional tests were performed wherein the metalizing compositionscontaining alloy powders were heated to temperatures just below thosetemperatures at which the alloy powders would have melted and formedglobules. The adhesive and solderability properties observed were betterthan those obtained when firing at 1050 C. Two examples of these testsare set forth hereinafter.

Example 4 A metalizing composition consisting of 90 parts of agold-platinum alloy containing 25% platinum, 10 parts of the preferredvitreous binder and 50 parts of an 8% solution of ethylcellulose inbeta-terpineol was prepared, screen-stencilled onto an aluminasubstrate, fired and dipsoldered. A tinned copper conductor was solderedthereto and tested with an Instron tester. The procedure followed wasthe same as that employed in obtaining th data reported in FIGURES 1 and2 with the exception that the metalizing composition was fired at 1150C. The Instron tester read 3,750 p.s.i. prior to failure.

Example 5 A metalizing composition consisting of 90 parts of agold-palladium alloy containing 25% palladium, 10 parts of the preferredvitreous binder and 50 parts of an 8% solution of ethylcellulose inbeta-terpineol was prepared, screen-stencilled onto an aluminasubstrate, fired and dip-soldered. A tinned copper conductor wassoldered thereto and tested with an Instron tester. The procedurefollowed was the same as that employed in obtaining the data reported inFIGURES 1 and 2 with the exception that the metal composition was firedat 1375 C. The Instron tester read 3,750 p.s.i. prior to failure.

Metalizing compositions comprising gold alloys of platinum and palladiumcontaining the preferred vitreous binder and organic vehicle have beenfound to provide excellent results when the constituents of thecomposition are present within the range of 63% to 80% alloy powder,0.5% to 10% cadmium borate frit, 2% to 15% bismuth oxide and 5% to 35%of a vehicle consisting of an 8% solution of ethylcellulose inbeta-terpineol. Of the compositions contained within this range thosecompositions which exhibit the most desirable electrical and mechanicalcharacteristics are grouped around the metalizing composition having70.20% alloy powder, 2.24% cadmium borate frit, 8.96% bismuth oxide and18.60% vehicle consisting of an 8% solution of ethylcellulose inbeta-terpineol.

The metalizing compositions to be used in the printing of conductivecircuit paths which need not be soldered can have a ratio of noble metalalloy to vitreous binder varied beyond the limits of the solderablealloy compositions area depicted in FIGURES 1 and 2. The amount ofvitreous binder employed must, however, be maintained at a level whichwill provide adequate adhesion, i.e., above about 2.5% of the solids ofthe metalizing composition. To provide adequate electrical conductivitythe percentage of vitreous binder in the solid content of the metalizingcomposition should not exceed about 30%. The precentages of one of themetals present in the metal alloy can range from about 5% to 95%.

The metal alloy powders used in the compositions of this inventionhaving one metal component thereof present in the alloy in the amount offrom 5% to 95%, in addition to being used to form conductors, can alsobe used with vitreous binders to form resistors. Metalizing compositionshaving vitreous binder to metal alloy ratios in the range of from 95:5to 20:80 have been found satisfactory, and provide a Wide range ofresistive values.

Examples of different materials and amounts thereof used in theformation of resistor metalizing compositions are set forth below.

Example 6 2.3 parts of a 64.5% Ag solution prepared by dissolving silvernitrate crystals in water were mixed with 3.6 parts of a 46.3% Pdsolution, prepared by dissolving palladium nitrate crystals in water,the volume thereof was adjusted to 100 cc. A solution of grams ofhypophosphorous acid in 100 ml. of water was used to precipitate analloy powder of 50% Ag and 50% Pd which was mixed with a frit having thecomposition 3.9 parts of CaO, 0.8 part of BaO, 27.7 parts of ZnO, 21.7parts of SiO 26.7 parts of B 0 8.7 parts of Na O, 0.7 part of PbO, 5.8parts of A1 0 and 4.0 parts of ZrO in the ratio of 40 parts of alloypowder to 60 parts of frit. 70 parts of the above mixture of frit andalloy powder were mixed with parts of an 8% solution of ethylcellulosein beta-terpineol.

Example 7 parts of the gold-platinum alloy powder consisting of 80%platinum, made in accordance with the procedure of Example 1, but using168 grams of the platinum solution and 32 grams of the gold solution,were mixed with 60 parts of the frit used in Example 6. 70 parts of theresulting mixture of alloy powder and frit were mixed with 30 parts ofan 8% solution of ethylcellulose in betaterpineol, to provide ametalizing composition for the printing of resistive paths.

Example 8 40 parts of the gold-palladium alloy consisting of 80%palladium, prepared in accordance with the procedure of Example 2, butusing 87 grams of palladium solution and 13 grams of the gold solution,were mixed with 60 parts of the frit used in Example 6. 70 parts of theresulting mixture of frit and alloy powder were mixed with 30 parts ofan 8% solution of ethylcellulose in beta-terpineol, to provide ametalizing composition for the printing of resistive paths.

Metalizing compositions useful for application to unfired dielectriclayers to provide capacitors consist essentially of noble metal alloypowders and inert vehicles. Vitreous binders are not required andgenerally not used. Examples of this aspect of the invention are setforth below.

Example 9 The silver-palladium alloy powder of Example 3 above, wasdispersed by hand mixing in a vehicle consisting of a 10% solution ofethylcellulose in butyl Cellosolve acetate to give a screen-stencilpaste consisting of by weight metal alloy powder and 50% by weightvehicle.

This paste was screened onto a 0.0025 inch thick unfired layer of bariumtitanate that had been formed by spraying an aqueous slurry of finelydivided barium titanate onto a substrate and then drying. The alloypaste, which covered an area of 1 cm. in diameter, was dried, thencovered with a second layer of titanate slurry and the process repeateduntil the desired number of alternate layers of dielectric and electrodewere built up. As is well known in such capacitor construction,alternate electrodes are exposed on opposite sides of the capacitorstructure. The composite structure was then fired at 1350-1450" C. forone hour. Leads were attached to the exposed electrode layers atopposite sides of the fired capacitor by silvering with a silver pasteand again fired at 760 C. and then soldered. FIGURES 3 and 4 illustratea capacitor constructed by this method. The capacitance of the capacitorwas 10,000 picofarads per layer and the dissipation factor was less than2%. This indicates that the alloy metalizing composition formed acontinuous conductive layer reasonably free from voids.

A similar experiment with an /20 mixture of pure palladium particles andpure silver particles (as distinguished from the alloy) in an equalamount of a 10% solution of ethycellulose in butyl Cellosolve acetateproved itself to be substantially useless as a capacitor electrodemetalizing composition when fired to a high temperature (over 1200 C.)At any temperature equal to or higher than the melting point of silver(about 960 C.), the melted silver, as a result of its surface tension,draws into tiny globules with the result that an undesirablenoncontinuous metallic electrode is obtained.

Example 10 A metalizing composition consisting of 50 parts of agold-palladium alloy containing 20% gold mixed with 50 parts of a 10%solution of ethylcellulose in butyl Cellosolve acetate was used inconjunction with a barium titanate slurry similarly as in the twoexamples immediately above to form a capacitor. The composite structurewas fired at about 1400 C. for one hour. On testing, the capacitorshowed a capacitance of 7,000 picofarads per layer and the dissipationfactor was about 2%.

Example 11 Still another capacitor was made in accordance with theprocedure of Example 9, but using a metalizing composition consisting of50 parts of a gold-platinum alloy containing 15% gold in 50 parts of a10% solution of ethylcellulose in butyl Cellosolve acetate. Thiscapacitor was formed using a firing temperature of 1400 C. for one hour.It exhibited a capacitance of 8,000 picofarads per layer and adissipation factor of about 2%.

Inasmuch as the metalizing compositions employed in the manufacture ofcapacitors need not be soldered and are maintained in place by thedielectric substrates in contact therewith, the noble metal alloy maycontain from 5% to 95% of either metal.

In preparing silver-palladium alloys which are to be used in metalizingcompositions which are to be fired at temperatures about 1300 C., theratio of silver-palladium in the alloy powder should be between 5 to 40%silver and 95 to 60% palladium. At 40% by weight of silver, the alloyhas a melting point near 1320 C. Metalizing compositions of 30 to 60% ofthese silver palladium alloy powders of a particle size not exceeding 5microns and preferably of an average particle size of 0.1 to 0.5 micron,dispersed in 70 to 40% of an inert liquid organic vehicle can be appliedby screen-stencilling most readily and result in excellent capacitors.

All percentages, parts and proportions of ingredients of materials setforth in the specification above and claims which follow, unlessotherwise stated, are percentages, parts and proportions by weight.

Having described various embodiments of the invention, for purposes ofillustration rather than limitation, what is claimed is as follows:

I claim:

1. A noble metal alloy metalizing composition suitable for use in theformation of capacitor electrodes comprising 30-90% solids content whichcomprises a noble metal alloy powder having particles of an irregularshape with at least of said alloy particles being of a size not greaterthan 5 microns, and wherein the alloy powder consists essentially of twonoble metals selected from the group consisting of silver, gold,platinum and palladium with one of the metals of the alloy being presenttherein in an amount within the range of from 595%, said solids beingdispersed in 10-70% of an inert liquid organic vehicle.

2. The metalizing composition of claim 1 wherein the particle size ofthe alloy powder does not exceed about 5 microns.

3. The metalizing composition of claim 2 wherein the average particlesize of the alloy powder is within the range of 0.1 to 0.5 micron.

4. The metalizing composition of claim 1 further comprising a vitreousbinder wherein the vitreous binder powder is present in an amount withinthe range of 2.5 to 95% of the combined weight of alloy powder andvitreous binder.

5. The metalizing composition of claim 4 suitable for use in theproduction of solderable conductors wherein one of the metals of thealloy powder is present in the alloy in an amount within the range ofabout 87.5% and 12.5% and wherein the vitreous binder constitutes inexcess of about 5% of the combined amount of alloy powder and vitreousbinder.

6. The metalizing composition of claim 4 wherein the noble metal alloyis platinum-gold wherein the amount of platinum in the alloy is Withinthe range of 15 to 85 and wherein the vitreous binder constitutes from 5to 30% of the combined weight of the alloy powder and vitreous binder.

7. The metalizing composition of claim 4 wherein the noble metal alloypowder is platinum-palladium and wherein the amount of platinum in thealloy is within the range of to 85% and wherein the vitreous binder constitutes from 5 to 30% of the combined weight of the alloy powder andvitreous binder.

8. The metalizing composition of claim 4 wherein the noble metal alloypowder is platinum-silver wherein the amount of platinum present in thealloy is within the range of to 85% and wherein the vitreous binderconstitutes from 5 to 30% of the combined weight of the alloy powder andvitreous binder.

9. The metalizing composition of claim 4 wherein the noble metal alloypowder is palladium-gold wherein the amount of palladium present in thealloy is within the range of 10 to 85 and wherein the vitreous binderconstitutes from 5 to of the combined weight of the alloy powder andvitreous binder.

10. The metalizing composition of claim 4 wherein the noble metal alloypowder is palladium-silver wherein the amount of palladium present inthe alloy is Within the range of 10 to 85% and wherein the vitreousbinder constitutes from 5 to 20% of the combined weight of the alloypowder and vitreous binder.

11. A palladium-silver alloy metalizing composition suitable for use inthe formation of capacitor electrodes comprising to 60% of apalladium-silver powder of a particle size not exceeding about 5 micronsand containing 5 to silver and 95 to palladium dispersed in to 40% of aninert liquid organic vehicle.

12. A palladium-silver alloy metalizing composition suitable for use inthe formation of capacitor electrodes comprising 30 to 60% of aprecipitated palladium-silver alloy powder having an average particlesize of 0.1 to 0.5 micron and containing 5 to 40% silver and 95 to 60%palladium dispersed in 70 to 40% of an inert liquid organic vehicle.

References Cited UNITED STATES PATENTS 2,950,996 8/1960 Place et al252-514 XR 3,172,753 3/1965 Walsh -.55 XR 1,165,448 12/1915 Richter75-172 2,129,721 9/1938 Wise 75-172 2,694,016 11/1954 Craven et a1117-227 2,793,273 5/1957 Underwood et a1. 252-514 2,924,540 2/1960DAndrea 252-514 X MURRAY KATZ, Primary Examiner.

LEON D. ROSDOL, Examiner.

I. D. WELSH, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,385,799 May 28 1968 Lewis C. Hoffman It is certified that error appears inthe above identified patent and that said Letters Patent are herebycorrected as shown below: Column 3, line 49, "relaive" should readrelative Column 4 line 69 "terpinelo'f should read terpineol Columr 5,line 17, "perified" should read prefired line 21, "of" should read online 22, "viterous" should read vitreous Column 6, line 32, "aalloy"should read alloy Column 9, line 5, "64.5" should read 63.5 Column 12,line 8, after "powder insert .having an irregular shape and line 16,after "having" insert an irregular shape and Signed and sealed this 25thday of November 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER,

Attesting Officer Commissioner of Patents

1. A NOBLE METAL ALLOY METALIZING COMPOSITION SUITABLE FOR USE IN THEFORMATION OF CAPACITOR ELECTRODES COMPRISING 30-90% SOLIDS CONTENT WHICHCOMPRISES A NOBLE METAL ALLOY POWDER HAVING PARTICLES OF AN IRREGULARSHAPE WITH AT LEAST 90% OF SAID ALLOY PARTICLES BEING OF A SIZE NOTGREATER THAN 5 MICRONS, AND WHEREIN THE ALLOY POWDER CONSISTSESSENTIALLY OF TWO NOBLE METALS SELECTED FROM THE GROUP CONSISTING OFSILVER, GOLD, PLATINUM AND PALLADIUM WITH ONE OF THE METALS OF THE ALLOYBEING PRESENT THEREIN IN AN AMOUNT WITHIN THE RANGE OF FROM 5-95%, SAIDSOILIDS BEING DISPERSED IN 10-70% OF AN INERT LIQUID ORGNIC VEHICLE.